Third generation (3G) mobile systems, such as, for instance, universal mobile telecommunication systems (UMTS) standardized within the third generation partnership project (3GPP) have been based on wideband code division multiple access (WCDMA) radio access technology. Today, 3G systems are being deployed on a broad scale all around the world. After enhancing this technology by introducing high-speed downlink packet access (HSDPA) and an enhanced uplink, also referred to as high-speed uplink packet access (HSUPA), the next major step in evolution of the UMTS standard has brought the combination of orthogonal frequency division multiplexing (OFDM) for the downlink and single carrier frequency division multiplexing access (SC-FDMA) for the uplink. This system has been named long term evolution (LTE) since it has been intended to cope with future technology evolutions.
The LTE system represents efficient packet based radio access and radio access networks that provide full IP-based functionalities with low latency and low cost. The downlink will support data modulation schemes QPSK, 16QAM, and 64QAM and the uplink will support QPSK, 16QAM, and at least for some devices also 64QAM, for physical data channel transmissions. The term “downlink” denotes direction from the network to the terminal. The term “uplink” denotes direction from the terminal to the network.
LTE's network access is to be extremely flexible, using a number of defined channel bandwidths between 1.4 and 20 MHz, contrasted with UMTS terrestrial radio access (UTRA) fixed 5 MHz channels. Spectral efficiency is increased by up to four-fold compared with UTRA, and improvements in architecture and signaling reduce round-trip latency. Multiple Input/Multiple Output (MIMO) antenna technology should enable 10 times as many users per cell as 3GPP's original WCDMA radio access technology. To suit as many frequency band allocation arrangements as possible, both paired (frequency division duplex FDD) and unpaired (time division duplex TDD) band operation is supported. LTE can co-exist with earlier 3GPP radio technologies, even in adjacent channels, and calls can be handed over to and from all 3GPP's previous radio access technologies.
An LTE network architecture including network entities and interfaces between them is exemplified in FIG. 1. As can be seen in FIG. 1, the LTE architecture supports interconnection of different radio access networks (RAN) such as UTRAN or GERAN (GSM EDGE Radio Access Network), which are connected to the EPC via the Serving GPRS Support Node (SGSN). In a 3GPP mobile network, the mobile terminal 110 (called User Equipment, UE, or device) is attached to the access network via the Node B (NB) in the UTRAN and via the evolved Node B (eNB) in the E-UTRAN access. The NB and eNB 120 entities are known as base station in other mobile networks. There are two data packet gateways located in the EPS for supporting the UE mobility—Serving Gateway (SGW) 130 and Packet Data Network Gateway 160 (PDN-GW or shortly PGW). Assuming the E-UTRAN access, the eNB entity 120 may be connected through wired lines to one or more SGWs via the 51-U interface (“U” stays for “user plane”) and to the Mobility Management Entity 140 (MME) via the S1-MMME interface. The SGSN 150 and MME 140 are also referred to as serving core network (CN) nodes.
As shown above, the E-UTRAN consists of an eNodeB, providing the E-UTRA user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towards the user equipment (UE). The eNodeB (eNB) hosts the Physical (PHY), Medium Access Control (MAC), Radio Link Control (RLC) and Packet Data Control Protocol (PDCP) layers that include the functionality of user-plane header-compression and encryption. It also offers Radio Resource Control (RRC) functionality corresponding to the control plane. It performs many functions including radio resource management, admission control, scheduling, enforcement of negotiated uplink Quality of Service (QoS), cell information broadcast, ciphering/deciphering of user and control plane data, and compression/decompression of downlink/uplink user plane packet headers. The eNodeBs are interconnected with each other by means of the X2 interface.
FIG. 2 illustrates structure of a component carrier in LTE Release 8. The downlink component carrier of the 3GPP LTE Release 8 is sub-divided in the time-frequency domain in so-called sub-frames each of which is divided into two downlink slots, one of which is shown in FIG. 2 as 220 corresponding to a time period Tslot. The first downlink slot comprises a control channel region within the first OFDM symbol(s). Each sub-frame consists of a given number of OFDM symbols in the time domain, each OFDM symbol spanning over the entire bandwidth of the component carrier. In particular, the smallest unit of resources that can be assigned by a scheduler is a resource block also called physical resource block (PRB). A PRB 230 is defined as NsymbDL consecutive OFDM symbols in the time domain and NscRB consecutive sub-carriers in the frequency domain. In practice, the downlink resources are assigned in resource block pairs. A resource block pair consists of two resource blocks. It spans NscRB consecutive sub-carriers in the frequency domain and the entire 2·NsymbDL modulation symbols of the sub-frame in the time domain. NsymbDL may be either 6 or 7 resulting in either 12 or 14 OFDM symbols in total. Consequently, a physical resource block 230 consists of NsymbDL×NscRB resource elements corresponding to one slot in the time domain and 180 kHz in the frequency domain (further details on the downlink resource grid can be found, for example, in 3GPP TS 36.211, “Evolved universal terrestrial radio access (E-UTRA); physical channels and modulations (Release 10)”, version 10.4.0, 2012, Section 6.2, freely available at www.3gpp.org, which is incorporated herein by reference). While it can happen that some resource elements within a resource block or resource block pair are not used even though it has been scheduled, for simplicity of the used terminology still the whole resource block or resource block pair is assigned. Examples for resource elements that are actually not assigned by a scheduler include reference signals, broadcast signals, synchronization signals, and resource elements used for various control signal or channel transmissions.
The number of physical resource blocks NRBDL in downlink depends on the downlink transmission bandwidth configured in the cell and is at present defined in LTE as being from the interval of 6 to 110 (P)RBs. It is common practice in LTE to denote the bandwidth either in units of Hz (e.g. 10 MHz) or in units of resource blocks, e.g. for the downlink case the cell bandwidth can equivalently expressed as e.g. 10 MHz or NRBDL=50 RB.
A channel resource may be defined as a “resource block” as exemplary illustrated in FIG. 3 where a multi-carrier communication system, e.g. employing OFDM as for example discussed in the LTE work item of 3GPP, is assumed. More generally, it may be assumed that a resource block designates the smallest resource unit on an air interface of a mobile communication that can be assigned by a scheduler. The dimensions of a resource block may be any combination of time (e.g. time slot, sub-frame, frame, etc. for time division multiplex (TDM)), frequency (e.g. subband, carrier frequency, etc. for frequency division multiplex (FDM)), code (e.g. spreading code for code division multiplex (CDM)), antenna (e.g. Multiple Input Multiple Output (MIMO)), etc. depending on the access scheme used in the mobile communication system.
The data are mapped onto physical resource blocks by means of pairs of virtual resource blocks. A pair of virtual resource blocks is mapped onto a pair of physical resource blocks. The following two types of virtual resource blocks are defined according to their mapping on the physical resource blocks in LTE downlink: Localised Virtual Resource Block (LVRB) and Distributed Virtual Resource Block (DVRB). In the localised transmission mode using the localised VRBs, the eNB has full control which and how many resource blocks are used, and should use this control usually to pick resource blocks that result in a large spectral efficiency. In most mobile communication systems, this results in adjacent physical resource blocks or multiple clusters of adjacent physical resource blocks for the transmission to a single user equipment, because the radio channel is coherent in the frequency domain, implying that if one physical resource block offers a large spectral efficiency, then it is very likely that an adjacent physical resource block offers a similarly large spectral efficiency. In the distributed transmission mode using the distributed VRBs, the physical resource blocks carrying data for the same UE are distributed across the frequency band in order to hit at least some physical resource blocks that offer a sufficiently large spectral efficiency, thereby obtaining frequency diversity.
In 3GPP LTE Release 8 the downlink control signalling is basically carried by the following three physical channels:                Physical control format indicator channel (PCFICH) for indicating the number of OFDM symbols used for control signalling in a sub-frame (i.e. the size of the control channel region);        Physical hybrid ARQ indicator channel (PHICH) for carrying the downlink ACK/NACK associated with uplink data transmission; and        Physical downlink control channel (PDCCH) for carrying downlink scheduling assignments and uplink scheduling assignments.        
The PCFICH is sent from a known position within the control signalling region of a downlink sub-frame using a known pre-defined modulation and coding scheme. The user equipment decodes the PCFICH in order to obtain information about a size of the control signalling region in a sub-frame, for instance, the number of OFDM symbols. If the user equipment (UE) is unable to decode the PCFICH or if it obtains an erroneous PCFICH value, it will not be able to correctly decode the L1/L2 control signalling (PDCCH) comprised in the control signalling region, which may result in losing all resource assignments contained therein.
The PDCCH carries control information, such as, for instance, scheduling grants for allocating resources for downlink or uplink data transmission. The PDCCH for the user equipment is transmitted on the first of either one, two or three OFDM symbols according to PCFICH within a sub-frame.
Physical downlink shared channel (PDSCH) is used to transport user data. PDSCH is mapped to the remaining OFDM symbols within one sub-frame after PDCCH. The PDSCH resources allocated for one UE are in the units of resource block for each sub-frame.
Physical uplink shared channel (PUSCH) carries user data. Physical Uplink Control Channel (PUCCH) carries signalling in the uplink direction such as scheduling requests, HARQ positive and negative acknowledgements in response to data packets on PDSCH, and channel state information (CSI).
FIG. 3 schematically illustrates an example of mapping of data onto a physical channel in LTE. It is noted that this example is a simplified mapping for illustrational purposes only. User data (IP packets) may be generated by the user application. They may include speech, video, text, or any other media possibly compressed and encapsulated into other protocols before forming the IP packets. The IP packets are in EUTRAN further processed on the PDCP layer resulting in addition of a PDCP header. The PDCP packets formed in this manner are further segmented and/or reassembled (reassembling being shown in the figure) into RLC packets to which an RLC header is added. One or more RLC packets are then encapsulated into a MAC packet including also a MAC header and padding, if necessary. The MAC packet is also called “transport block”. Thus, a transport block is from the point of view of the physical layer a packet of user data entering the physical layer. There are predefined transport block sizes (TBS) which may be used in LTE. The transport block is then within one transmission time interval (TTI) mapped onto the subframes on the physical layer (PHY). Details of the mapping of data starting with transport blocks up to the interleaving is shown in FIGS. 5.2.2-1 and 5.3.2-1 and described in the related description of the 3GPP TS 36.212, v.10.4.0, “Evolved universal terrestrial radio access (E-UTRA); Multiplexing and channel coding” available freely at www.3gpp.org and incorporated herein by reference, for the uplink and downlink transmission of user data respectively. Furthermore, the physical channel mapping is described in detail in FIGS. 6.3-1 and FIGS. 5.3-1 for downlink and uplink, respectively, and the related description in 3GPP TS 36.211, v10.4.0. An functional overview of uplink and downlink shared channel is furthermore given in sections 6.1.1 and 6.2.1 (respectively) of 3GPP TS 36.302, v10.3.0, “Evolved Universal Terrestrial Radio Access (E-UTRA); Services provided by the physical layer”.
The MAC layer provides a data transfer service for the RLC layer through logical channels. Logical channels are either Control Logical Channels which carry control data such as RRC signalling, or Traffic Logical Channels which carry user plane data. Broadcast Control Channel (BCCH), Paging Control channel (PCCH), Common Control Channel (CCCH), Multicast Control Channel (MCCH) and Dedicated Control Channel (DCCH) are Control Logical Channels. Dedicated Traffic channel (DTCH) and Multicast Traffic Channel (MTCH) are Traffic Logical Channels. Data from the MAC layer is exchanged with the physical layer through Transport Channels. Data is multiplexed into transport channels depending on how it is transmitted over the air. Transport channels are classified as downlink or uplink as follows. Broadcast Channel (BCH), Downlink Shared Channel (DL-SCH), Paging Channel (PCH) and Multicast Channel (MCH) are downlink transport channels, whereas the Uplink Shared Channel (UL-SCH) and the Random Access Channel (RACH) are uplink transport channels. A multiplexing is then performed between logical channels and transport channels in the downlink and uplink respectively.
A possibility provided by the LTE in order to improve battery lifetime is the discontinuous transmission (DTX) and reception (DRX). In order to provide a reasonable battery consumption of the terminal (UE), LTE Rel-8/9 as well as Rel-10 provides a concept of discontinuous reception (DRX). Accordingly, the terminal does not have to regularly monitor the control channels but rather can switch off the transmission and the reception over long periods and needs to activate the transceiver only at predefined or required time instances.
The principle of link adaptation is fundamental to the design of a radio interface which is efficient for packet-switched data traffic. Unlike the early versions of UMTS (Universal Mobile Telecommunication System), which used fast closed-loop power control to support circuit-switched services with a roughly constant data rate, link adaptation in LTE adjusts the transmitted data rate (modulation scheme and channel coding rate) dynamically to match the prevailing radio channel capacity for each user.
For the downlink data transmissions in LTE, the eNodeB typically selects the modulation scheme and code rate (MCS) depending on a prediction of the downlink channel conditions. An important input to this selection process is the Channel State Information (CSI) feedback (mentioned above) transmitted by the User Equipment (UE) in the uplink to the eNodeB.
Channel state information is used in a multi-user communication system, such as for example 3GPP LTE to determine the quality of channel resource(s) for one or more users. In general, in response to the CSI feedback the eNodeB can select between QPSK, 16-QAM and 64-QAM schemes and a wide range of code rates. This CSI information may be used to aid in a multi-user scheduling algorithm to assign channel resources to different users, or to adapt link parameters such as modulation scheme, coding rate or transmit power, so as to exploit the assigned channel resources to its fullest potential.
The uplink and downlink resource grants (grants enabling the UE to transmit data in downlink and uplink, respectively) are transmitted from the eNodeB to the UE in a downlink control information (DCI) via PDCCH. The downlink control information may be transmitted in different formats, depending on the signaling information necessary. In general, the DCI may include:                a resource block assignment (RBA),        modulation and coding scheme (MCS).        
It may include further information, depending on the signaling information necessary, as also described in Section 9.3.2.3 of the book “LTE: The UMTS Long Term Evolution from theory to practice” by S. Sesia, I. Toufik, M. Baker, April 2009, John Wiley & Sons, ISBN 978-0-470-69716-0, which is incorporated herein by reference. For instance, the DCI may further include HARQ related information such as redundancy version (RV), HARQ process number, or new data indicator (NDI); MIMO related information such as pre-coding; power control related information, etc.
As described above, in order to inform the scheduled users about their allocation status, transport format and other data-related information (e.g. HARQ information, transmit power control (TPC) commands), L1/L2 control signaling is transmitted on the downlink along with the data. L1/L2 control signaling is multiplexed with the downlink data in a subframe, assuming that the user allocation can basically change from subframe to subframe. It should be noted that user allocation might also be performed on a TTI (Transmission Time Interval) basis, where the TTI length can be in general a multiple of the subframes or correspond to a subframe. The TTI length may be fixed in a service area for all users, may be different for different users, or may even by dynamic for each user. Generally, the L1/2 control signaling needs only be transmitted once per TTI. Without loss of generality, the following assumes that a TTI is equivalent to one subframe.
The L1/L2 control signaling is transmitted on the Physical Downlink Control Channel (PDCCH). A PDCCH carries a message as a Downlink Control Information (DCI), which in most cases includes resource assignments (allocations) and other control information for a mobile terminal or groups of UEs. In general, several PDCCHs can be transmitted in one subframe. It should be noted that in 3GPP LTE, assignments for uplink data transmissions, also referred to as uplink scheduling grants or uplink resource assignments, are also transmitted on the PDCCH. Generally, the information sent on the L1/L2 control signaling for assigning uplink or downlink radio resources (particularly LTE(-A) Release 10) can be categorized to the following items:                User identity, indicating the user that is allocated. This is typically included in the checksum by masking the CRC with the user identity. Then, the users (UEs) perform blind decoding by demasking the identities transmitted in the search space (i.e. in the resources configured as search space in which the respective terminals have to monitor the control information whether there is data for them).        Resource allocation information, indicating the resources (Resource Blocks, RBs) on which a user is allocated. Note, that the number of RBs on which a user is allocated can thus be dynamic. In particular, the number of the resource blocks (frequency domain) is carried by the resource allocation information. The position in the time domain (subframe) is given by the subframe in which the PDCCH is received and a predefined rule (the resources are allocated fixed number of subframes after the PDCCH subframe)        Carrier indicator, which is used if a control channel transmitted on a first carrier assigns resources that concern a second carrier, i.e. resources on a second carrier or resources related to a second carrier if carrier aggregation is applied.        Modulation and coding scheme that determines the employed modulation scheme and coding rate (length of the transport block to be coded).        HARQ information, such as a new data indicator (NDI) and/or a redundancy version (RV) that is particularly useful in retransmissions of data packets or parts thereof. In particular, new data indicator indicated whether the allocation is for an initial transmission of data or for a retransmission of data. Redundancy version indicates the coding applied to the retransmitted data (in LTE incremental redundancy combining is supported, meaning that each retransmission may include the data of the first transmission differently coded, i.e. may include parity bits which together with the already received transmission/retransmission(s) finally enable decoding).        Power control commands to adjust the transmit power of the assigned uplink data or control information transmission.        Reference signal information such as the applied cyclic shift and/or orthogonal cover code index, which are to be employed for transmission or reception of reference signals related to the assignment.        Uplink or downlink assignment index that is used to identify an order of assignments, which is particularly useful in TDD systems.        Hopping information, e.g. an indication whether and how to apply resource hopping in order to increase the frequency diversity.        CSI request, which is used to trigger the transmission of channel state information in an assigned resource.        Multi-cluster information, which is a flag used to indicate and control whether the transmission occurs in a single cluster (contiguous set of RBs) or in multiple clusters (at least two non-contiguous sets of contiguous RBs). Multi-cluster allocation has been introduced by 3GPP LTE-(A) Release 10.        
It is to be noted that the above listing is non-exhaustive, and not all mentioned information items need to be present in each PDCCH transmission depending on the DCI format that is used.
Downlink control information occurs in several formats that differ in overall size and also in the information contained in its fields. The different DCI formats that are currently defined for LTE are as follows and described in detail in 3GPP TS 36.212, “Multiplexing and channel coding”, section 5.3.3.1 (available at http://www.3gpp.org and incorporated herein by reference). For further information regarding the DCI formats and the particular information that is transmitted in the DCI, please refer to the technical standard or to LTE—The UMTS Long Term Evolution—From Theory to Practice, Edited by Stefanie Sesia, Issam Toufik, Matthew Baker, Chapter 9.3, incorporated herein by reference. For instance, DCI Format 0 is used for the transmission of resource grants for the PUSCH, using single-antenna port transmissions in uplink transmission mode 1 or 2.
In order for the UE to identify whether it has received a PDCCH transmission correctly, error detection is provided by means of a 16-bit CRC appended to each PDCCH (i.e. DCI). Furthermore, it is necessary that the UE can identify which PDCCH(s) are intended for it. This could in theory be achieved by adding an identifier to the PDCCH payload; however, it turns out to be more efficient to scramble the CRC with the “UE identity”, which saves the additional overhead. The CRC may be calculated and scrambled as defined in detail by 3GPP in TS 36.212, Section 5.3.3.2 “CRC attachment”, incorporated hereby by reference. The section describes how error detection is provided on DCI transmissions through a Cyclic Redundancy Check (CRC). A brief summary is given below. The entire payload is used to calculate the CRC parity bits. The parity bits are computed and attached. In the case where UE transmit antenna selection is not configured or applicable, after attachment, the CRC parity bits are scrambled with the corresponding RNTI.
The scrambling may further depend on the UE transmit antenna selection, as apparent from TS 36.212. In the case where UE transmit antenna selection is configured and applicable, after attachment, the CRC parity bits are scrambled with an antenna selection mask and the corresponding RNTI. As in both cases the RNTI is involved in the scrambling operation, for simplicity and without loss of generality the following description of the embodiments simply refers to the CRC being scrambled (and descrambled, as applicable) with an RNTI, which should therefore be understood as notwithstanding e.g. a further element in the scrambling process such as an antenna selection mask.
Correspondingly, the UE descrambles the CRC by applying the “UE identity” and, if no CRC error is detected, the UE determines that PDCCH carries its control information intended for itself. The terminology of “masking” and “de-masking” is used as well, for the above-described process of scrambling a CRC with an identity. The “UE identity” mentioned above with which the CRC of the DCI may be scrambled can also be a SI-RNTI (System Information Radio Network Temporary Identifier), which is not a “UE identity” as such, but rather an identifier associated with the type of information that is indicated and transmitted, in this case the system information. The SI-RNTI is usually fixed in the specification and thus known a priori to all UEs.
The physical downlink control channel (PDCCH) carries e.g. scheduling grants for allocating resources for downlink or uplink data transmission. Multiple PDCCHs can be transmitted in a subframe. The PDCCH for the user equipments is transmitted on the first NsymbPDCCH OFDM symbols (usually either 1, 2 or 3 OFDM symbols as indicated by the PCFICH, in exceptional cases either 2, 3, or 4 OFDM symbols as indicated by the PCFICH) within a subframe, extending over the entire system bandwidth; the system bandwidth is typically equivalent to the span of a cell or component carrier. The region occupied by the first NsymbPDCCH OFDM symbols in the time domain and the NRBDL×NscRB subcarriers in the frequency domain is also referred to as PDCCH region or control channel region. The remaining NsymbPDCCH=2·NsymbDL−NsymbPDCCH OFDM symbols in the time domain on the IV subcarriers in the frequency domain is referred to as the PDSCH region or shared channel region (see below).
For a downlink grant (i.e. resource assignment) on the physical downlink shared channel (PDSCH), the PDCCH assigns a PDSCH resource for (user) data within the same subframe. The PDCCH control channel region within a subframe consists of a set of Control Channel Elements, CCEs where the total number of CCEs in the control region of subframe is distributed throughout time and frequency control resource. Multiple CCEs can be combined to effectively reduce the coding rate of the control channel. CCEs are combined in a predetermined manner using a tree structure to achieve different coding rate. Control channel elements are separately allocable units smaller than the entire physical resource block. They enable finer resource assignment for the control channel in which smaller amounts of data are transported.
On a transport channel level, the information transmitted via the PDCCH is also referred to as L1/L2 control signaling (for details on L1/L2 control signaling see above).
There is a particular predefined timing relation between uplink resource assignments received in a subframe and the corresponding uplink transmission in PUSCH. Details are given in TS 36.213 v11.1.0 “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures (Release 11)” Chapter 8.0 “UE procedure for transmitting the physical uplink shared channel” incorporated herewith by reference. In particular, Table 8-2 of TS 36.213 defines the parameter k for the TDD configurations 0-6, where k indicates the positive offset of the target of an uplink resource allocation received in a subframe; for TDD configuration 0 there is additional definition of the timing for uplink subframes 3 and 8, omitted herewith for simplicity. For instance, the parameter k is 6 for subframe 1 of TDD configuration 1, meaning that an uplink resource allocation received in subframe 1 of TDD configuration 1 is intended for subframe 1+6=7 of TDD configuration 1, which indeed is an uplink subframe, etc.
The resource block assignment specifies the physical resource blocks which are to be used for the transmission in uplink or downlink.
The modulation and coding scheme defines the modulation scheme employed for the transmission such as QPSK, 16-QAM or 64-QAM. The lower the order of the modulation, the more robust is the transmission. Thus, 64-QAM is typically used when the channel conditions are good. The modulation and coding scheme also defines a code rate for a given modulation. The code rate is chosen depending on the radio link conditions: a lower code rate can be used in poor channel conditions and a higher code rate can be used in the case of good channel conditions. “Good” and “bad” here is used in terms of the signal to noise and interference ratio. The finer adaptation of the code rate is achieved by puncturing or repetition of the generic rate depending on the error correcting coder type.
For uplink resource assignments (for transmissions on the Physical Uplink Shared CHannel (PUSCH)) signaled on PDCCH in LTE, the L1/L2 control information does not contain a HARQ process number, since a synchronous HARQ protocol is employed for LTE uplink. The HARQ process to be used for an uplink transmission is given by the timing. Furthermore it should be noted that the redundancy version (RV) information is jointly encoded with the transport format information, i.e. the RV info is embedded in the transport format (TF) field. The TF respectively modulation and coding scheme (MCS) field has for example a size of bits, which corresponds to 32 entries. 3 TF/MCS table entries are reserved for indicating RVs 1, 2 or 3. The remaining MCS table entries are used to signal the MCS level (TBS) implicitly indicating RV0.
For details on the TBS/RV signaling for uplink assignments on PDCCH please see 3GPP TS 36.213, “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures”, version 3GPP TS 36.213, v.10.4.0, 2012 (available at http://www.3gpp.org and incorporated herein by reference). The size of the CRC field of the PDCCH is 16 bits.
For downlink assignments (PDSCH) signaled on PDCCH in LTE the Redundancy Version (RV) is signaled separately in a two-bit field. Furthermore the modulation order information is jointly encoded with the transport format information. Similar to the uplink case there is 5 bit MCS field signaled on PDCCH. Three of the entries are reserved to signal an explicit modulation order, providing no Transport format (Transport block) info. For the remaining 29 entries modulation order and Transport block size info are signaled.
In order to increase frequency diversity, LTE provides a possibility of hopping. Two hopping modes are supported, hopping only between subframes (inter-subframe hopping) and hopping both between and within subframes (inter- and intra-subframe hopping). In case of intra-subframe hopping, a frequency hop occurs at the slot boundary in the middle of the subframe. This provides frequency diversity within a codeword. Inter-subframe hopping provides frequency diversity between HARQ retransmissions of a transport block, as the frequency allocation hops every allocated subframe.
In order to increase the uplink coverage for power limited terminals or coverage scenarios, so-called TTI bundling has been introduced into Release 8 of LTE. The power limited terminals may be, for instance, the UEs present in the cell edge. A power-limited coverage scenario occurs, for instance, at the cell edge, where the signal received from the network (base station, eNB) is rather weak and the terminal has to increase its power and/or set a more robust modulation and coding scheme in order to enable the base station to receive its signal in the uplink. However, the possibility of increasing the transmission power is limited since it causes interference for other devices in this cell and possibly in the neighbor cells as well. Thus, the power limitation is mainly due to the limited interference to be generated. A further advantage of TTI bundling is also the reduction of overhead to avoid RLC segmentation.
FIG. 4 illustrates a TTI bundling mechanisms. The data to be transmitted are first coded 401. After the coding, the data is mapped onto four consecutive subframes 405, which are referred to as four bundled subframes or simply as a TTI bundle with a length of four subframes. For instance, in a power-limited scenario a single transport block from the MAC layer may be transmitted repeatedly in the four consecutive bundled subframes in order to increase the robustness of the transmission. The numbers indicated in the subframe-representing squares indicate the number of the HARQ process. The four subframes of the bundle belonging to the first process are denoted by 0000, the four subframes of the bundle belonging to the second process are denoted 1111, etc. Thus, in FIG. 4, four HARQ processes 0 to 3 are configured. For instance, the configuration of the number of processes in LTE is always 8 in the uplink per serving cell if no TTI-bundling is applied. If TTI-bundling is applied, there are 4 HARQ processes.
During the TTI bundling, the efficiency of signaling is increased by providing only one set of control signaling for the transmission of the entire bundle. For instance, the terminal will only receive PDCCH uplink grants once per entire bundle. Moreover, within a bundle, HARQ retransmissions are non-adaptive and triggered without waiting for HARQ feedback from previous transmissions. This is illustrated in FIG. 4, in which within the bundle data transmitted in the first four subframes 405 an error was detected. Accordingly, a negative acknowledgement (NACK) is transmitted from the network to the terminal. After receiving the negative acknowledgement, the terminal retransmits the data of all four subframes 405 in a new bundle of TTIs within the subframes 415.
In general, dynamic scheduling of TTI, bundling may be supported, which means that a TTI bundle may be scheduled at any time by using the signaling channel PDCCH. For instance, the starting point for transmitting the TTI bundle may be defined by such signaling. In particular, the PDCCH includes an uplink grant for the bundle into a PDCCH which is transmitted in a certain subframe. A fixed pattern is defined or configured by higher layers, which specifies the number of subframes between the certain grant (i.e. the reception of the grant by the terminal) and the transmission of the bundle for which the grant was received. Such a fixed timing pattern enables reducing the signaling overhead since the grant does not need to explicitly specify the number of subframe in which the bundle is to be transmitted. Rather, the position of the grant in the time domain (in terms of subframe number) and the defined gap between the reception of grant and the transmission of data, enable to unambiguously determine the time point for the bundle transmission. Accordingly, for instance, the terminal always transmits a bundle of N subframes after M subframes from receiving the grant for the bundle. The parameter M is set according to the system parameters such as round-trip time and processing delay. According to 3GPP TS 36.213, v. 8.8.0 “Physical layer procedures”, September 2009, in particular Section 8 (available freely at www.3gpp.orq and incorporated herein by reference), for FDD (Frequency Division Duplex) mode and subframe (TTI) bundling operation, the UE will upon detection of a PDCCH with DCI format 0 in subframe n intended for the UE, and/or a PHICH transmission in subframe n−5 intended for the UE, adjust the corresponding first PUSCH transmission in the bundle in subframe n+4 according to the PDCCH and PHICH information. Thus, the timing in the Rel-8 LTE is fixed, i.e. for TTI Bundling operation, the data is transmitted from the terminal to the network 4 subframes after receiving a grant and 9 subframes after negative acknowledgement (in PHICH).
Apart from a possible fixed pattern (timing) between the reception of a grant and the transmission of the bundle data, the timing pattern may also be specified for the events of the retransmission protocol. For instance, the transmission of acknowledgement (positive or negative) may also be timed fixedly with respect to receiving of the grant and/or transmitting the data. Similarly, the data retransmission may be timed fixedly with respect to receiving of the feedback (acknowledgement) and/or the data transmission and/or the grant reception. In the LTE as currently defined, the fixed grant and HARQ process timing is specified for the downlink and uplink shared channel.
However, the application of TTI bundling also raises some problems connected with the specification of the terminal behavior at various possible network behaviors and configurations. Currently, within the standardization, dynamic scheduling of TTI bundling has been agreed in order to support scheduling flexibility and efficient system resource utilization. A flexible scheduling opportunity and efficient resource utilization are required to enhance the system capacity, especially when considering a high volume of UEs and Voice over IP services. The current standard does not specify the terminal behavior for the case when an uplink grant is indicated, which may cause different TTI HARQ processes/bundles to collide. Two TTI bundles collide when their (re)transmission times at least partially overlap. This may be an overlap of (re)transmissions of two active HARQ processes or an overlap between one active process (i.e. HARQ buffer for the process is non-empty and data is transmitted) and one non-active process (which does not transmit the bundle on a particular occasion).
Accordingly, it is possible that some terminals will always ignore “shifting” PDCCH (and make the original/previous HARQ Process PUSCH transmission) in case different TTI bundles collide. However, the UE behavior may be implemented in any way deciding to follow or not to follow the “shifting” PDCCH received and causing TTI bundle collision. This may lead to misinterpretation of received PDCCH and de-synchronization of the timing between the terminal and the network. Since the network may not know the UE implementation i.e. whether or not the UE would shift the PUSCH transmissions of process X on to the extended TTIs (starting overlapping TTIs with the next HARQ process) inside Process X+1, the decoding at the network side may subsequently fail. This may even lead the UE to exceed the maximum allowed re-transmissions allowed for any process, maxHARQ-Tx, leading to radio link failure and/or reset/re-establishment of protocol entities.